How to get a value from onPostExecute() to if I have a separate class that extends an <AsyncTask> class?

Issue

I got a problem on getting the value given by the onPostExecute() method of the AsyncTask class, why is it not displaying to the textview?

CollegeBulletinListFragment.java

package com.example.navigationdrawerexample;


import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.util.ArrayList;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Fragment;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.StrictMode;
import android.app.Fragment;
import android.app.FragmentManager;
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

public class CollegeBulletinListFragment extends Fragment implements OnClickListener{
    public CollegeBulletinListFragment(){
    }

    TextView kem;
    TextView headlinehead;
    TextView shortdesc;
    TextView headlinesender;
    LinearLayout llist;
    ImageButton img;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_collegebulletinlist, container, false);


        headlinehead = (TextView) rootView.findViewById(R.id.headlinetitle);
        String c = getArguments().getString("passingWord");
        llist = (LinearLayout) rootView.findViewById(R.id.lllist);
        int colval = this.setTextAndColorsToHead(c);
        String firstFlag = "headline";

        String secondFlag = "list";
        Connector connect= new Connector(getActivity().getApplicationContext(),colval,secondFlag);
        connect.execute("");

        String txt = connect.getJSON();
        headlinehead.setText(txt);
        return rootView;
    }


    public int setTextAndColorsToHead(String arg){
        int collegeval = 0;
        if (arg.equals("GN")){
            kem.setText("General News");
        } else if (arg.equals("CCS")){
            kem.setText("College of Computer Studies");
            collegeval = 1;
        } else if (arg.equals("COE")){
            kem.setText("College of Engineering");
            collegeval = 2;
        } else if (arg.equals("COED")){
            kem.setText("College of Education");
            collegeval = 4;
        } else if (arg.equals("CON")){
            kem.setText("College of Nursing");
            collegeval = 3;
        } else if (arg.equals("CBA")){
            kem.setText("College of Business and Accountancy");
            collegeval = 5;
        } else if (arg.equals("CAS")){
            kem.setText("College of Arts and Sciences");
            collegeval = 6;
        } else if (arg.equals("CIHM")){
            kem.setText("College of International and Hospitality Management");
            collegeval = 7;
        } 
        return collegeval;
    }
}

Here is the Connector class that extends <AsyncTask>, on the onPostExecute method, the string of the request is returned, I stored the string on the response variable through setJSON() method and I created a getJSON() method for me to be able to get the string response of my request in CollegeBulletinListFragment..

Connector.java

package com.example.navigationdrawerexample;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URL;
import java.util.ArrayList;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.ProgressDialog;
import android.content.Context;
import android.graphics.Typeface;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup.LayoutParams;
import android.widget.LinearLayout;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class Connector extends AsyncTask<String,Void,String>{
    private Context context;
    private int collegeactive;
    private String flag;

    private String response;
    public Connector(Context context,int college, String flag){
        this.context = context;
        this.collegeactive = college;
        this.flag = flag;   
    }


    protected void onPreExecute(){
        //Toast.makeText(context, "Please Wait", Toast.LENGTH_LONG).show();
        //ProgressBar pb = new ProgressBar(this.context);
    }


    @Override
    protected String doInBackground(String... arg0) {
        // TODO Auto-generated method stub

        try{
            String link = "";
            if (flag ==  "headline"){
                link = "http://rtu-astronet.com/emag/functions.php?action=printHeadline&coll_id="+collegeactive;
            } else if (flag == "list"){
                link = "http://rtu-astronet.com/emag/functions.php?action=printArticlePerCollege&collegeid="+collegeactive+"&acadornot=1";
            }
            URL url = new URL(link);
            HttpClient client = new DefaultHttpClient();
            HttpGet request = new HttpGet();
            request.setURI(new URI(link));
            HttpResponse response = client.execute(request);
            BufferedReader in = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));

            StringBuffer sb = new StringBuffer("");
            String line = "";

            while ((line = in.readLine()) != null) {
                sb.append(line);
                //break;
            }

            in.close();
            return sb.toString();
        } catch(Exception e){
             return new String("Exception: " + e.getMessage());
        }
    }


    @Override
    protected void onPostExecute(String result) {
        result = "{ \n \"Data\": \n " + result + " \n }";
        this.setJSON(result);
    }


    private void setJSON(String result){
        this.response = result;
    }

    public String getJSON(){
        return this.response;
    }

}

But, there is no string response shown in the textview headlinehead, why is it like that? What are the possible solutions for this?

Solution

You can achieve this will callback listener.

public class Connector extends AsyncTask<String,Void,String>{
    private OnPostExecuteListener onPostExecuteListener;
     /**
     * The callback interface
     */
    public interface OnPostExecuteListener {
        void onPostExecute(String result);
    }

    public void setOnPostExecuteListener(OnPostExecuteListener listener){
        this.onPostExecuteListener = listener;
    }

    @Override
    protected void onPostExecute(String result) {
       result = "{ \n \"Data\": \n " + result + " \n }";
       if(onPostExecuteListener !=null){
             onPostExecuteListener.onPostExecute(result);
       }
       this.setJSON(result);
    }

}

In your fragment class

public class CollegeBulletinListFragment extends Fragment implements OnClickListener, Connector.OnPostExecuteListener {

   @Override
   public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
       Connector connect= new Connector(getActivity().getApplicationContext(),colval,secondFlag);
       connect.setOnPostExecuteListener(this); // set callback listener
       connect.execute("");
   }

   @Override
   public void onPostExecute(String result){
      // do something with onPostExecute result.
   }

}

Answered By - Dhaval Patel